In a system having a computing device connected to a volume comprising stored data, a data set can be accessed directly by requesting the specific volume serial number using a fetching program. The request may be sent to the Volume Table Of Contents (VTOC), which in turns finds the exact location of the data set as well as the data set's physical information, such as record length and blocksize. However, a typical data storage system can comprise a thousand or more volumes. Additionally, many data storage systems implement an automated data allocation product that selects a volume to store data rather than allowing a user to specify preferences. The information stored on such data storage systems is typically organized into catalogs that can be utilized to locate data sets.
A catalog, in basic terms, comprises a data set containing information to locate other data sets. In turn, a data set is a unit of data storage typically consisting of a collection of logically related data in prescribed arrangements, and is stored on one or more external storage volumes. The catalog itself may not be stored on the same volumes as the data sets it describes and is capable of referring to thousands of data sets stored across numerous volumes.
For data storage systems, catalogs are critical resources. When a catalog breaks or is mistakenly deleted, a speedy and successful recovery is crucial for maintaining data access; a single user catalog could provide access to thousands of data sets supporting hundreds of applications. The most prudent course of action is to perform frequent and timely backups. However, businesses often operate storage systems for years without an incident, and therefore, do not appreciate the need to backup catalogs on a regular basis. When the business does suffer an incident, the backups, if they exist, may be too outdated to be useful. Not being prepared for such a failure, the business can incur substantial costs in terms of system downtime and the man hours involved in locating and rebuilding the catalog.
Clearly, there is a need for a method of forward catalog recovery, particularly when there are no recent backups, wherein that method minimizes down time and the time, effort, and resources, required to rebuild an accurate catalog.